1. Field of the Invention
The present invention relates to a thin film magnetic head that has a medium projection detection mechanism for detecting projections on a surface of a recording medium by discharging, and a head gimbal assembly and a magnetic disk device that include the thin film magnetic head.
2. Description of Related Art
In a magnetic disk device, a magnetic head is floated by an airflow that is created by rotation of a magnetic disk (or a recording medium) so that information is recorded on and reproduced from the magnetic disk. A flying height of the magnetic head (hereinafter flying height) is decreased with an increase in the high recording density of the magnetic disk. In recent years, the flying height has become smaller and smaller in size to approximately 10 nm or less. However, when the flying height is less than 10 nm, the magnetic head has a tendency to hit a projection on the magnetic disk surface. Therefore, there is a possibility that characteristics of the magnetic head may be changed due to the change in shape of the magnetic head caused by frictional heat and contact.
Because of the problem discussed above, in a recording medium magnetic disk, surface projections are miniaturized with a high precision surface treatment (burnish) so that, recently, a required projection height (ground height) may be less than 4 nm.
In order to float a head slider with a certain flying height, it is necessary that a flying force (lifting power) generated at an air bearing surface (ABS) of the head slider, a gravitational force of the head slider, and a total spring load (pressing load) force of a suspension attached to one end of the head slider are balanced out. Also, it is necessary that each of these forces or loads has a specified value.
When a reading element frequently hits a projection existing on a recording medium surface (medium projection), the element property deteriorates (property deterioration occurs). As a method to resolve this problem, there is the following method in which a track where the projection exists is not used. When the reading element hits the projection, a mapping in which the location of the projection exists on the recording medium surface is specified is performed by measuring a resistance change due to the element's temperature change. However, when the reading element is a so called tunneling magnetoresistive (TMR) element, there is a disadvantage in that accurate mapping is difficult. Because an oxide layer, such as Al2O3, MgO, TiOX, or the like, is used as a barrier film to be sandwiched by two ferromagnetic layers and has a small temperature dependence with respect to the resistance so that the resistance change is small, it is hard to detect when the reading element hits the projection. Since the temperature coefficient of resistance of a TMR element in which MgO or the like is used for the barrier film is close to zero, the resistance change that is caused by a temperature increase due to the hitting is minimal so that it is hard to detect the hitting of the projection.
For a giant magnetoresistive (GMR) element in which an intermediate layer made of a metal layer, such as Cu, is sandwiched by two ferromagnetic layers, an operation based on the method of making the mapping through the hitting between the element and projection cannot be said as the best method. Because a direction of a longitudinal bias that is applied in the track width direction with a hard magnet by plural hitting is changed, there is a possibility that the property degradation occurs.
In consideration of the situation described above, the present invention is provided. An object of the present invention is to provide a novel thin film magnetic head to detect a projection on a recording medium surface in a noncontacting manner and further enabling the mapping instead of the conventional mapping for the projection on the recording medium surface with contact. It is also an object to provide a head gimbal assembly and a magnetic disk device system that have the thin film magnetic head mentioned above.